Laser-engraveable elements

ABSTRACT

A laser-engraveable layer is used in a laser-engraveable element to provide relief images. The resulting laser-engraved elements can take various forms and can be used to apply various inks to receiver materials in an imagewise fashion. The laser-engraveable element has a thermally crosslinked laser-engraveable layer containing a crosslinked elastomeric fluoropolymer and a fluoro-functionalized near-infrared radiation absorber. The crosslinked fluoropolymer has a glass transition temperature of less than and including 0° C. and the crosslinked laser-engraveable layer is formed from a reactive fluoropolymer composition comprising a reactive fluoropolymer, the fluoro-functionalized near-infrared radiation absorber, and a compound that causes crosslinking of the reactive fluoropolymer during thermal curing. The reactive fluoropolymer can have a reactive group selected from the group consisting of: poly(tetrafluoroethylene oxide-co-difluoromethylene oxide) α,ω-diol bis(2,3-dihydroxypropyl ether), poly(tetrafluoroethylene oxide-co-dilfluoromethylene oxide) α,ω-diol, ethoxylated poly(tetrafluoroethylene oxide-co-difluoromethylene oxide) α,ω-diol, and a multifuncational (meth)acrylate end-functionalized derivative of one of such compounds.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of recently allowed U.S. patentapplication Ser. No. 13/456,323, filed Apr. 26, 2012 which is herebyincorporated herein by reference in its entirety.

FIELD OF THE INVENTION

This invention relates to laser-imageable (laser-engraveable)compositions and reactive fluoropolymer compositions used to make them.The laser-engraveable compositions can be used in relief-formingelements such as flexographic printing precursors. This invention alsorelates to methods of preparing these compositions.

BACKGROUND OF THE INVENTION

Relief images can be provided and used in various articles for manydifferent purposes. For example, the electronics, display, and energyindustries rely on the formation of coatings and patterns of conductivematerials to form circuits on organic and inorganic substrates. Suchcoatings and patterns are often provided using relief imaging methodsand relief image forming elements. There is also need for means toprovide fine wiring in various articles.

Flexography is a method of printing that is commonly used forhigh-volume printing runs. It is usually employed for printing on avariety of soft or easily deformed materials including but not limitedto, paper, paperboard stock, corrugated board, polymeric films, fabrics,metal foils, glass, glass-coated materials, flexible glass materials,and laminates of multiple materials. Coarse surfaces and stretchablepolymeric films are economically printed using flexography.

Flexographic printing members are sometimes known as “relief” printingmembers (for example, relief-containing printing plates, printingsleeves, or printing cylinders) and are provided with raised reliefimages onto which ink is applied for application to a printablematerial. While the raised relief images are inked, the relief “floor”should remain free of ink. The flexographic printing precursors aregenerally supplied with one or more imageable layers that can bedisposed over a backing layer or substrate. Flexographic printing alsocan be carried out using a flexographic printing cylinder or seamlesssleeve having the desired relief image.

Flexographic printing members can be provided from flexographic printingprecursors that can be “imaged in-the-round” (ITR) using either aphotomask or laser-ablatable mask (LAM) over a photosensitivecomposition (layer), or they can be imaged by direct laser engraving(DLE) of a laser-engraveable composition (layer) that is not necessarilyphotosensitive.

Gravure or intaglio printing members are also relief printing members inwhich the image to be printed comprises depressions or recesses on thesurface of the printing member, where the printing area is localized tothe areas of depression that define the pattern or image. The processfor using gravure or intaglio printing members is the reverse offlexographic relief printing wherein an image is raised above the floorof the flexographic printing member and the printing area is localizedat the contact area of the top surface protrusions.

Laser ablation or laser engraving can be used effectively with anappropriate laser-engraveable precursor to form images for either of theabove-mentioned printing processes.

Flexographic printing precursors having laser-ablatable layers aredescribed for example in U.S. Pat. No. 5,719,009 (Fan) where precursorsinclude a laser-ablatable mask layer over one or more photosensitivelayers. This publication teaches the use of a developer to removeunreacted material from the photosensitive layer, the barrier layer, andnon-ablated portions of the mask layer.

There has been a desire in the industry for a way to prepareflexographic printing members without the use of photosensitive layersthat are cured using UV or actinic radiation and that require liquidprocessing to remove non-imaged composition and mask layers and thatgenerate significant amount of liquid waste. Direct laser engraving ofprecursors to produce relief printing plates and stamps is known, butthe need for relief image depths greater than 500 μm creates aconsiderable challenge when imaging speed is also an importantcommercial requirement. In contrast to laser ablation of mask layersthat require low to moderate energy lasers and fluence, direct engravingof a relief-forming layer requires much higher energy and fluence. Alaser-engraveable layer must also exhibit appropriate physical andchemical properties to achieve “clean” and rapid laser engraving (highsensitivity) so that the resulting printed images have excellentresolution and durability.

A number of elastomeric systems have been described for construction oflaser-engraveable flexographic printing precursors. For example, U.S.Pat. No. 6,223,655 (Shanbaum et al.) describes the use of a mixture ofepoxidized natural rubber and natural rubber in a laser-engraveablecomposition. Engraving of a rubber is also described by S. E. Nielsen inPolymer Testing 3 (1983) pp. 303-310.

U.S. Pat. No. 4,934,267 (Hashimito) describes the use of a natural orsynthetic rubber, or mixtures of both, such as acrylonitrile-butadiene,styrene-butadiene and chloroprene rubbers, on a textile support. “LaserEngraving of Rubbers—The Influence of Fillers” by W. Kern et al.,October 1997, pp. 710-715 (Rohstoffe Und Anwendendunghen) describes theuse of natural rubber, nitrile rubber (NBR), ethylene-propylene-dieneterpolymer (EPDM), and styrene-butadiene copolymer (SBR) for laserengraving.

U.S. Pat. No. 5,798,202 (Cushner et al.) describes the use of reinforcedblock copolymers incorporating carbon black in a layer that is UV curedand remains thermoplastic. Such block copolymers are used in manycommercial UV-sensitive flexographic printing plate precursors. Aspointed out in U.S. Pat. No. 6,935,236 (Hiller et al.), such curingwould be defective due to the high absorption of UV as it traversesthrough the thick imageable layer. Although many polymers are suggestedfor this use in the literature, only extremely flexible elastomers havebeen used commercially because flexographic layers that are manymillimeters thick must be designed to be bent around a printing cylinderand secured with temporary bonding tape and both must be removable afterprinting.

U.S. Pat. No. 6,776,095 (Telser et al.) describes elastomers includingan EPDM rubber and U.S. Pat. No. 6,913,869 (Leinenbach et al.) describesthe use of an EPDM rubber for the production of flexographic printingplates having a flexible metal support. U.S. Pat. No. 7,223,524 (Hilleret al.) describes the use of a natural rubber with highly conductivecarbon blacks. U.S. Pat. No. 7,290,487 (Hiller et al.) lists suitablehydrophobic elastomers with inert plasticizers.

An increased need for higher quality flexographic printing precursorsfor laser engraving has highlighted the need to solve performanceproblems that were of less importance when quality demands were lessstringent. However, it has been especially difficult to simultaneouslyimprove the flexographic printing precursor in various propertiesbecause a change that can solve one problem can worsen or cause anotherproblem.

For example, the rate of imaging, edge sharpness, and cleanliness of thelaser-engraved image features are now important considerations in laserengraving of flexographic printing precursors and can be criticalparameters for high resolution printing performance. Although U.S. Pat.No. 7,290,487 (Hiller et al.) describes the use of hydrophobicelastomers for laser-engraving, such elastomers may be incompatible withmany radiation-absorbers, providing defective engraved features. Thereremains a need to provide a laser-engraveable composition that providessharp defect-free engraved image features.

Direct laser engraving has also been used to pattern various surfaces asdescribed in U.S. Patent Application Publication 2011/0086204 (Wohl, Jr.et al.).

There is an increasing need to control the wetting properties of thelaser-engraveable elements to enable controlled ink wetting of thelaser-engraved elements and controlled ink separation and depositionfrom the laser-engraved element to suitable receiver materials.

U.S. Patent 2010/0151387 describes the use of adding low molecularweight fluorinated acrylates or methacrylates to a photosensitiveprinting plate to modify the wetting properties of the plate. However,these polymers do not provide for the performance properties requiredfor a laser-engraveable printing element with differentiated ink wettingand release properties.

There continues to be a need to improve the sensitivity,manufacturability, and performance of laser-engraveable flexographicprinting precursors (or other patternable elements) usinglaser-engraveable compositions having suitable physical and chemicalproperties. There is a desire to improve sensitivity, to improveselectivity of ink wetting and transfer, to reduce imaging time, and toincrease the throughput of an imaging engraving apparatus. Also, thereis a desire to achieve flexographic printing plate or other patternableelements that will provide relief images with good quality solid areasand dot reproduction even when printing is performed at high speeds.

SUMMARY OF THE INVENTION

This invention provides a composition comprising:

1) a fluoropolymer (such as an elastomeric fluoropolymer), and

2) at least 1 weight % of a fluoro-functionalized near-infraredradiation absorber, based on the total dry composition weight.

In some embodiments, a composition of this invention comprises:

1) an elastomeric perfluoropolyether in an amount of at least 30 weight% and up to and including 99 weight %,

2) at least 1 weight % and up to and including 35 weight % of afluoro-functionalized carbon black, based on the total dry compositionweight, and

3) one or more of microspheres and inorganic solid or porous particles,in an amount of up to and including 50 weight %, based on total drycomposition weight,

wherein the weight ratio of the elastomeric perfluoropolyether to thefluoro-functionalized carbon black is from 19:1 to and including 4:1.

In addition, this invention provides a reactive fluoropolymercomposition comprising a reactive fluoropolymer, a fluoro-functionalizednear-infrared radiation absorber, and a compound that causescrosslinking of the reactive fluoropolymer during thermal curing.

This invention further provides a method for providing alaser-engraveable composition, comprising:

combining a reactive fluoropolymer, a fluoro-functionalizednear-infrared radiation absorber, and a compound that causescrosslinking of the reactive fluoropolymer during thermal curing, toform a reactive fluoropolymer composition, and

thermally curing the reactive fluoropolymer composition to provide alaser-engraveable composition comprising a fluoropolymer (such as anelastomeric fluoropolymer) and the near-infrared radiation absorber.

The present invention provides laser-engraveable compositions andmethods of making these compositions, which can be used inlaser-engraveable elements to provide relief images for a variety ofpurposes. For example, these laser-engraveable elements can be designedfor use as flexographic printing precursors. However, they can also bepatternable articles used to form patterned conductive articles that canbe incorporated into display devices, optical devices, solar panels, orelectronic devices.

The laser-engraveable compositions of this invention provide severaladvantages. For example, the fluoropolymer used to make thelaser-engraveable layer is mixed with a fluoro-functionalizednear-infrared radiation absorber (such as fluoro-functionalized carbonblack) that is well dispersed within the fluoropolymer to provide moreuniform laser engraving. Elastomeric fluoropolymers are particularlyuseful in the practice of this invention.

Furthermore, the low surface energy of the laser-engraveable layerformed using the composition of this invention has properties such asselective wetting and de-wetting of inks and solvent resistance.Moreover, the laser-engraveable layer can repel both hydrophobic andhydrophilic molecules (this property is sometimes known as“amphiphobicity”). This property can affect printing applications wherewetting behavior and other surface characteristics are important forprinting performance and properties.

DETAILED DESCRIPTION OF THE INVENTION Definitions

As used herein to define various components of the laser-engraveablecompositions and formulations, reactive fluoropolymer compositions,non-laser-engraveable compositions and layers, unless otherwiseindicated, the singular forms “a”, “an”, and “the” are intended toinclude one or more of the components (that is, including pluralityreferents).

Each term that is not explicitly defined in the present application isto be understood to have a meaning that is commonly accepted by thoseskilled in the art. If the construction of a term would render itmeaningless or essentially meaningless in its context, the termdefinition should be taken from a standard dictionary.

The use of numerical values in the various ranges specified herein,unless otherwise expressly indicated otherwise, are considered to beapproximations as though the minimum and maximum values within thestated ranges were both preceded by the word “about”. In this manner,slight variations above and below the stated ranges can be used toachieve substantially the same results as the values within the ranges.In addition, the disclosure of these ranges is intended as a continuousrange including every value between the minimum and maximum values.

Moreover, unless otherwise indicated, percentages refer to percents bytotal dry weight, for example, weight % based on total solids of alayer, composition, or formulation. Unless otherwise indicated, thepercentages can be the same for either the dry layer or the total solidsof a formulation or composition used to make a layer.

In some embodiments, the term “imaging” refers to ablation of thebackground areas while leaving intact the areas of the laser-engraveableelement that can be inked up and printed using a suitable ink, such asin flexographic printing members.

Alternatively the term “imaging” refers to ablation of the image areasthat can be inked up using a suitable ink (for printing) while leavingintact the areas of the laser-engraveable element that will not beprinted, such as in gravure or intaglio printing members.

The term “flexographic printing precursor” refers to some embodiments ofa non-imaged laser-engraveable element described herein. Theflexographic printing precursors include flexographic printing plateprecursors, flexographic printing sleeve precursors, and flexographicprinting cylinder precursors, all of which can be directlylaser-engraved to provide a relief image using a laser to have a minimumrelief depth of at least 10 μm and up to and including 4000 μm, or atleast 50 μm to and including 3000 μm. Such directly laser-engraveable,relief-forming precursors can also be known as “flexographic printingplate blanks”, “flexographic printing cylinders”, or “flexographicsleeve blanks”. The laser-engraveable flexographic printing precursorscan also have seamless or continuous forms.

The term “laser-engraveable” means that the laser-engraveable (orimageable) layer can be directly imaged using a suitable laser-engravingsource including infrared radiation lasers, for example carbon dioxidelasers and near-infrared radiation lasers such as Nd:YAG lasers, laserdiodes, and fiber lasers. Absorption of energy from these lasersproduces heat that causes rapid local changes in the laser-engraveablelayer so that the imaged regions are physically detached from the restof the layer or substrate and ejected from the layer and collected usingsuitable means. Non-imaged regions of the laser-engraveable layer arenot removed or volatilized to an appreciable extent and thus form theupper surface of the relief image that is the element printing surfacefor flexographic printing, for example, or non-printing surface forgravure or intaglio printing, for example. The breakdown is a violentprocess that includes eruptions, explosions, tearing, decomposition,fragmentation, oxidation, or other destructive processes that create abroad collection of solid debris and gases. This is distinguishablefrom, for example, image transfer. “Laser-ablative” and“laser-engraveable” can be used interchangeably in the art, but forpurposes of this invention, the term “laser-engraveable” is used todefine the imaging according to the present invention in which a reliefimage is formed in the laser-engraveable layer. It is distinguishablefrom image transfer methods in which ablation is used to materiallytransfer pigments, colorants, or other image-forming components. As usedherein “direct” laser engraving of the relief-forming layer isdistinguished from laser ablation of a thin layer to create a mask thatis used to control the application of curing radiation to underlyinglayers and is removed prior to printing.

Unless otherwise indicated, the terms “laser-engraveable composition”and “laser-engraveable layer formulation” are intended to be the same.

The “top surface” is equivalent to the “relief-image forming surface”and is defined as the outermost surface of the laser-engraveable elementand is generally the first surface that is struck by imaging (engraving)radiation during the laser-engraving process. The “bottom surface” isdefined as the surface of the laser-engraveable element that is mostdistant from the imaging radiation.

The term “elastomeric fluoropolymer” refers to fluoropolymers thatgenerally regain their original shape after being stretched orcompressed when the forces are removed. Generally, an elastomericmaterial is an amorphous polymer existing above its glass transitiontemperature at ambient or use temperatures. Typically, these polymersare crosslinked, either physically or chemically, and have highelasticity.

Uses

The laser-engraveable compositions of this invention can be used in manyways. The most likely use is to form flexographic printing precursors asdescribed herein. However, while the following disclosure is directedprimarily to flexographic printing precursors, it is to be understoodthat the present invention is not so limited. For example, thelaser-engraveable elements can also be used to provide relief images forgravure printing, intaglio printing, or relief images or patterns foroptical devices, electronic devices, display devices, or medicaldevices.

Flexographic Printing Precursors

The flexographic printing precursors are laser-engraveable to provide adesired relief image, and comprise at least one laser-engraveable layerthat is formed from a laser-engraveable composition of this inventionthat comprises one or more fluoropolymers (such as elastomericfluoropolymers) in a total amount of generally at least 30 weight % andup to and including 99 weight %, and more typically at least 50 weight %and up to and including 95 weight %, based on the total drylaser-engraveable composition or layer weight. The fluoropolymers aregenerally crosslinked, meaning that they have been polymerized orcrosslinked during thermal curing (described below).

The elastomeric fluoropolymers useful in this invention generally have aglass transition temperature (T_(g)) of less than 0° C. and typically atleast −100° C. and up to and including 0° C.

The elastomeric fluoropolymers can be prepared using various reactivefluoropolymers as described below. Examples of useful reactivefluoropolymers include but not limited to, poly(tetrafluoroethyleneoxide-co-difluoromethylene oxide) α,ω-diol bis(2,3-dihydroxypropylether), poly(tetrafluoroethylene oxide-co-dilfluoromethylene oxide)α,ω-diol, and ethoxylated poly(tetrafluoroethyleneoxide-co-difluoromethylene oxide) α,ω-diol, or the meth(acrylate)end-functionalized derivatives of the above compounds, but many otherswould be possible using the various reactive fluoropolymers andcompounds that cause crosslinking of the reactive fluoropolymers.

The reactive fluoropolymers useful in this invention generally havenumber average molecular weights (M_(n)) greater than 1000 g/mol and upto about 100,000 g/mol.

Other examples of useful elastomeric fluoropolymers include fluorocarbonrubbers and fluorosilicone rubbers.

Examples of useful non-elastomeric fluoropolymers include but are notlimited to, homopolymers and copolymers derived from one or more ofvinylidene fluoride, vinyl fluoride, tetrafluoroethylene,chlorotrifluoroethylene, perfluoroalkyl vinyl ethers, andhexafluoropropylene monomers and polymers containing trifluoromethylgroups. Examples of these include but are not limited to,polytetrafluoroethylene, polytetrafluoroethylene copolymers,polychlorotrifluoroethylene and polychlorotrifluoroethylene copolymers,perfluoroalkoxy polymers and perfluoroalkoxy copolymers,polyhexafluoropropylene and hexafluoropropylene copolymers, poly(vinylfluoride) and poly(vinyl fluoride) copolymers such as those listed underthe trademark Kynar®, poly(vinylidene fluoride) homo- and co-polymers,polyperfluorosulfonates, fluorinated polyacrylates, fluorinatedpolymethacrylates, fluorinated polystyrenes, fluorinated polyamides,fluorinated polyimides, fluorinated polyurethanes, and fluorinatedepoxides, and mixtures of any of these.

Although it is understood from this disclosure that laser-engraveableelastomeric fluoropolymer compositions of this invention are useful forflexible printing applications such as for flexographic printing, glassyor hard laser-engraveable (non-elastomeric) fluoropolymer compositionscan be used for alternate printing or patterning applications and forsurface energy control of the patterned printing members.

The laser-engraveable composition or layer also comprises at least 1weight % and up to and including 35 weight %, or typically at least 5weight % and up to and including 20 weight %, of one or morefluoro-functionalized near-infrared radiation absorbers (such as afluoro-functionalized carbon black), based on the total drylaser-engraveable composition or layer weight. The fluoro-functionalizednear-infrared radiation absorber is generally uniformly dispersed withinthe laser-engraveable composition.

These fluoro-functionalized near-IR, or IR radiation absorbersfacilitate or enhance laser engraving, and the fluoro-functionalizednear-infrared radiation absorbers have significant (perhaps maximum)absorption at wavelengths of at least 700 nm and higher in what is knownas the infrared portion of the electromagnetic spectrum. In particularlyuseful embodiments, the fluoro-functionalized near-infrared radiationabsorber has a λ_(max), in the near-infrared portion of theelectromagnetic spectrum having a λ_(max) of at least 700 nm or at least750 nm and up to and including 1400 nm. In particularly usefulembodiments, the fluoro-functionalized near-infrared radiation absorberhas an essentially panchromic absorption behavior that includesabsorption in the near-infrared portion of the electromagnetic spectrum.Mixtures of fluoro-functionalized near-infrared radiation absorbers andmixtures of fluoro-functionalized near-infrared radiation absorbers withnon-fluoro-functionalized near-infrared radiation absorbers can be usedif desired, and the individual materials can have the same or differentabsorption spectra. The absorbance of the fluoro-functionalizednear-infrared radiation absorber can be matched to the particularlaser-engraving radiation that is to be used.

Such fluoro-functionalized near-infrared radiation absorbers can be afluoro-functionalized carbon black, fluoro-functionalized carbonnanotube, fluoro-functionalized graphene, or fluoro-functionalized dye,or mixtures or combinations of any of these materials. Such materialscan be purchased from various commercial sources such as CabotCorporation (Boston, Mass.), or prepared using known procedures andcommercially available starting materials. For example,fluoro-functionalized carbon blacks can be prepared by the reaction offluoro-substituted aryl diazonium salts with commercially availablecarbon blacks using known methods as described for example in U.S. Pat.No. 5,554,739 (Belmont) and U.S. Pat. No. 6,399,202 (Yu et al.).

Thus, in some embodiments, the fluoropolymer (such as an elastomericfluoropolymer) and the fluoro-functionalized near-infrared radiationabsorber can be the only two essential components for providing alaser-engraveable composition or laser-engraveable layer. However, thelaser-engraveable composition used to prepare the laser-engraveablelayer can include residual, but generally non-functional, amounts of thecompounds that provide crosslinking during thermal curing of thereactive fluoropolymers (described below).

The weight ratio of the fluoropolymer (such as an elastomericfluoropolymer) to the fluoro-functionalized near-infrared absorber inthe laser-engraveable composition or layer is generally from 99:1 to andincluding 1.4:1, or typically from 19:1 to and including 4:1.

In some embodiments, the laser-engraveable composition or layer canoptionally include up to 50 weight %, based on the total dry compositionor layer weight of additional materials selected from the groupconsisting of hollow, solid, or porous particles, surfactants,plasticizers, lubricants, and microspheres. Such materials includeelastomeric or non-elastomeric resins that are not fluoropolymersincluding but not limited to, commercial rubbers such as EPDM, SBR, NBR,commercial thermoplastic elastomers, such as Kraton™ SBS, SEBS, SISproducts, copolymers of styrene and butadiene, copolymers of isopreneand styrene, styrene-butadiene-styrene block copolymers,styrene-isoprene-styrene copolymers, other polybutadiene or polyisopreneelastomers, nitrile elastomers, polychloroprene, polyisobutylene andother butyl elastomers, elastomers containing chlorosulfonatedpolyethylene, polysulfide, polyalkylene oxides, or polyphosphazenes,elastomeric polymers of (meth)acrylates, elastomeric polyesters, andother similar polymers known in the art. Still other useful elastomericresins include vulcanized rubbers, such as Nitrile (Buna-N), Naturalrubber, Neoprene or chloroprene rubber, silicone rubber, SBR(styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber),ethylene-propylene rubber, and butyl rubber.

Other optional resins are non-elastomeric resins including but notlimited to, thermosetting or thermoplastic urethane resins that arederived from the reaction of a polyol (such as polymeric diol or triol)with a polyisocyanate or the reaction of a polyamine with apolyisocyanate, styrenic polymers, acrylate and methacrylate polymersand copolymers, olefinic polymers and copolymers, and epoxide polymers.

It is understood that the mixture of the fluoropolymer and otheroptional elastomeric or non-elastomeric resins must form a compatiblemixture. A particularly useful “compatible” mixture would be one whereinthe elastomeric resin(s) form isolated phase separated domains withaverage dimensions from 0.01 μm to and including 10 μm in diameterwithin the fluoropolymer.

It is also possible that the fluoro-functionalized near-infraredradiation absorber is dispersed non-uniformly within thelaser-engraveable layer, and being present in a concentration that isgreater near the bottom surface of the laser-engraveable layer than thetop surface. This concentration profile can provide a laser energyabsorption profile as the depth into the laser-engraveable layerincreases. In some instances, the concentration changes continuously andgenerally uniformly with depth. In other instances, the concentration isvaried with layer depth in a step-wise manner. Further details of sucharrangements are provided in U.S. Pat. No. 8,114,572 (Landry-Coltrain etal.) that is incorporated herein by reference.

The laser-engraveable composition or layer can optionally includeorganic or inorganic filler materials selected from the group consistingof hollow, solid, or porous particles, surfactants, and microspheres.Useful inorganic fillers and other particles include but not limited to,various aluminas or silicas (treated, fumed, or untreated), calciumcarbonate, magnesium oxide, talc, barium sulfate, kaolin, bentonite,hallosite and other clays, zinc oxide, zirconium oxide, mica, titaniumdioxide, and mixtures thereof. Particularly useful inorganic fillers aresilica, calcium carbonate, and alumina, including fine particulatesilica, fumed silica, porous silica, surface treated silica, sold asAerosil® from Degussa, Utrasil® from Evonik, and Cab-O-Sil® from CabotCorporation, micropowders such as amorphous magnesium silicate cosmeticmicrospheres sold by Cabot and 3M Corporation, calcium carbonate andbarium sulfate particles and microparticles, zinc oxide, and titaniumdioxide, or mixtures of two or more of these materials.

When present, the amount of the inorganic fillers in thelaser-engraveable composition or layer is up to and including 50 weight%.

The laser-engraveable composition or layer can optionally comprisemicrocapsules that are dispersed generally uniformly within thelaser-engraveable composition. These “microcapsules” can also be knownas “hollow beads”, “hollow spheres”, “microspheres”, microbubbles”,“micro-balloons”, “porous beads”, or “porous particles”. Somemicrocapsules include a thermoplastic polymeric outer shell and a coreof either air or a volatile liquid such as isopentane or isobutane. Themicrocapsules can comprise a single center core or many voids (pores)within the core. The voids can be interconnected or non-connected. Forexample, microcapsules can be designed like those described in U.S. Pat.No. 4,060,032 (Evans) and 6,989,220 (Kanga) in which the shell iscomposed of a poly[vinylidene-(meth)acrylonitrile] resin orpoly(vinylidene chloride), or as plastic micro-balloons as described forexample in U.S. Pat. No. 6,090,529 (Gelbart) and U.S. Pat. No. 6,159,659(Gelbart). Some useful microcapsules are the EXPANCEL® microspheres thatare commercially available from Akzo Noble Industries (Duluth, Ga.),Dualite and Micropearl polymeric microspheres that are available fromPierce & Stevens Corporation (Buffalo, N.Y.), hollow plastic pigmentsthat are available from Dow Chemical Company (Midland, Mich.), and theorganic porous particles that are described in copending and commonlyassigned U.S. Ser. Nos. 13/192,531 and 13/192,533, (both filed Jul. 28,2011 by Landry-Coltrain and Nair).

Upon laser-engraving, the microspheres that are hollow or filled with aninert solvent, burst and give a foam-like structure or facilitateablation of material from the laser-engraveable layer because theyreduce the energy needed for ablation.

Other optional addenda in the laser-engraveable composition or layer caninclude but are not limited to, dyes, antioxidants, antiozonants,stabilizers, dispersing or processing aids, surfactants, waxes,lubricants, adhesion promoters, and plasticizers as long as they do notinterfere with laser-engraving efficiency. Examples of plasticizers caninclude low molecular weight polyolefins, polyesters, and polyacrylates,fluorinated compounds (other than those described as essentialcomponents), silicone compounds, non-crosslinked liquid rubbers andoils, liquid ethylene-propylenes, liquid polybutylene, liquidpolypropylene, or mixtures these materials.

The laser-engraveable layer incorporated into the laser-engraveableelements (such as flexographic printing precursors) has a dry thicknessof at least 0.05 μm and up to and including 4,000 μm, or typically of atleast 50 μm and up to and including 3,000 μm, or at least 300 μm and upto and including 3,000 μm.

The total dry thickness of the entire laser-engraveable elements (suchas flexographic printing precursors) is at least 300 μm and up to andincluding 6,000 μm or typically at least 1,000 μm and up to andincluding 3,000 μm. Flexographic printing sleeve precursors cangenerally have a laser-engraveable layer having a dry thickness of atleast 2 mm and up to and including 20 mm. Flexographic printingcylinders can have a suitable laser-engraveable layer dry thickness.

Multiple layers of the laser-engraveable layer can be disposed one ontop of the other in order to create a thicker compositelaser-engraveable layer. These multiple laser-engraveable layers can beidentical in composition or thickness, or they can differ in compositionin that they contain differing amounts and types of components (forexample, particulates, microcapsules, fluoro-functionalizednear-infrared radiation absorbers, and fluoropolymers), or in thickness.For example, a laser-engraveable layer containing hollow microspheres ormicrobubbles can be disposed under an uppermost laser-engraveable layerthat does not contain hollow microspheres. A skilled worker could designmany different arrangements of such multiple laser-engraveable layers.

While a single laser-engraveable layer is present in most flexographicprinting precursors, there can be multiple laser-engraveable layersformed from the same or different laser-engraveable compositions, suchlayers having the same or different fluoropolymers prepared from thesame or different reactive fluoropolymers, and the same or differentfluoro-functionalized near-infrared radiation absorbers. Thus, in someembodiments, there are two or more layers in the laser-engraveableelement including at least one laser-engraveable layer according to thisinvention. For example, there can be an additional or secondlaser-engraveable layer that is contiguous to a first laser-engraveablelayer, both of which laser-engraveable layers are prepared according tothis invention and can be laser-engraved at the same or different times.

In other embodiments, a non-laser engraveable layer can be arrangedcontiguous to a single laser-engraveable layer.

In still other embodiments, a non-fluoropolymer-containing laserengraveable layer can be arranged contiguous to afluoropolymer-containing laser-engraveable layer.

The laser-engraveable elements also include embodiments in which thelaser-engraveable layer is a first laser-engraveable layer, and thelaser-engraveable element further comprises a second layer-engraveablelayer that is contiguous to the first laser-engraveable layer, whereinthe second laser-engraveable layer is either a fluoropolymer-containinglaser-engraveable layer according to the present invention or anon-fluoropolymer-containing laser-engraveable layer.

Other embodiments include alternating laser-engraveable layers andnon-laser-engraveable layers, for example such as a sandwich of at leastthree layers, such as a first laser-engraveable layer, anon-laser-engraveable layer, and a second laser-engraveable layer. Askilled worker in the art could design any number of alternativearrangements of suitable layers as embodiments of the present invention.

In most embodiments, the laser-engraveable layer according to thisinvention is the outermost layer of the laser-engraveable elements,including embodiments where the laser-engraveable layer is disposed on aflexographic printing cylinder as a sleeve. However, in someembodiments, the laser-engraveable layer can be located underneath anoutermost capping smoothing layer that provides additional smoothness ordifferent ink reception and release. This smoothing layer can have ageneral dry thickness of at least 1 μm and up to and including 200 μm.

The flexographic printing precursors can optionally comprise anelastomeric rubber layer that is considered a “compressible” layer (alsoknown as a cushioning layer) and is disposed over the substrate andunder a laser-engraveable layer. In most embodiments, the compressiblelayer is disposed directly on the substrate and the laser-engraveablelayer is disposed directly on the compressible layer. While thecompressible layer can be non-laser-engraveable, in some embodiments,the compressible layer comprises one or more components that make itlaser-engraveable.

The compressible layer can also have microvoids or microspheresdispersed within the one or more elastomeric rubbers. In mostembodiments, the microvoids or microspheres are uniformly dispersedwithin the elastomeric rubbers. Useful microspheres are described aboveas “microcapsules”, “hollow beads”, “hollow spheres”, microbubbles”,“micro-balloons”, “porous beads”, or “porous particles”, which aredispersed (generally uniformly) within the one or more elastomericrubbers in the compressible layer. The compressible layer can alsocomprise other addenda such as filler materials and addenda describedabove for the laser-engraveable layer.

The dry thickness of the compressible layer is generally at least 50 μmand up to and including 4,000 μm, or typically at least 100 μm and up toand including 2,000 μm.

The laser-engraveable or patternable elements (such as flexographicprinting precursors) described herein can have a suitable dimensionallystable, non-laser-engraveable substrate having an imaging side and anon-imaging side. The substrate has at least one laser-engraveable layerdisposed over it on the imaging side of the substrate. Suitablesubstrates include dimensionally stable polymeric films, hightemperature polymeric films, chemically resistant films, aluminum sheetsor cylinders, transparent foams, ceramics, glasses, porous glasses,fabrics, or laminates of polymeric films (from condensation or additionpolymers) and metal sheets such as a laminate of a polyester andaluminum sheet or polyester/polyamide laminates, or a laminate of apolyester film and a compliant or adhesive support. Polyester,polycarbonate, poly(vinyl chloride), and polystyrene films are typicallyused. Useful polyesters include but are not limited to poly(ethyleneterephthalate) and poly(ethylene naphthalate). Other high temperaturepolymers useful as high temperature films include but are not limitedto, polyetherimides, polyimides (such as Kapton™ films) PEEK(polyetheretherketone), polysulfone, polyethersulfone,polyphenylsulfone, and polyphenylenesulfide.

The substrates can have any suitable thickness, but generally they areat least 0.01 mm or at least 0.05 mm and up to and including 5 mm thick.

Some particularly useful substrates comprise one or more layers of ametal, fabric, or polymeric film, glass, porous glass, ceramic, or acombination thereof. For example, a fabric web can be applied to apolyester or aluminum support using a suitable adhesive. For example,the fabric web can have a thickness of at least 0.1 mm and up to andincluding 0.5 mm, and the polyester support thickness can be at least100 μm and up to and including 200 μm or the aluminum support can have athickness of at least 200 μm and up to and including 400 μm. Forexample, a glass substrate can have a thickness of at least 100 μm andup to and including 5 mm. The dry adhesive thickness can be at least 10μm and up to and including 300 μm.

A thin conductive layer or film of, for example,poly(3,4-ethylenedioxythiophene) (PEDOT), polyacetylene, polyaniline,polypyrrole, or other polythiophenes, indium tin oxide (ITO), orgraphene, can be disposed between the substrate and a laser engraveablelayer.

There can be a non-laser-engraveable backcoat on the non-imaging side ofthe substrate that can comprise a soft rubber or foam, or othercompliant layer. This non-laser-engraveable backcoat can provideadhesion between the substrate and printing press rollers and canprovide extra compliance to the resulting laser-engraved member, or forexample to reduce or control the curl of a resulting laser-engravedmember. Alternatively, this backcoat can be laser-engraveable so as toprovide the capability for writing specific information, productidentification, classification, or other metadata.

The laser engraveable element or patternable element (such as aflexographic printing precursor) can be subjected to mechanical grindingby known methods in the art using commercially available machines suchas belt grinders, cylindrical grinders using an abrasive wheel, orpaper. Grinding can be done on either the top surface of the imagingside of the laser-engraveable element or the bottom surface of thelaser-engraveable element, prior to the optional introduction of asupport, in order to ensure thickness uniformity, or it can be done onthe laser-engraveable surface to achieve a desired surface roughnessthat will improve ink wetting or transfer.

Preparation of Laser-Engraveable Elements (and Patternable Elements)

Preparation of the laser-engraveable elements (or patentable elements)is illustrated as follows with respect to flexographic printingprecursors but other laser-engraveable elements and patternable elementscan be similarly prepared.

One or more reactive fluoropolymers, one or more fluoro-functionalizednear-infrared radiation absorbers (for example, thefluoro-functionalized carbon black, fluoro-functionalized carbonnanotubes, fluoro-functionalized graphene, or fluoro-functionalized dye,or a combination of any of these materials described above), and one ormore compounds that cause crosslinking of the reactive fluoropolymerduring thermal curing, and any optional materials (for example, one ormore materials selected from the group consisting of hollow, solid, orporous particles, surfactants, plasticizers, lubricants, non-fluorinatedresins, and microspheres as described above), are combined (mixed orformulated) to form a reactive fluoropolymer composition. Combiningthese components can be carried out by melt-mixing using any suitablemechanical mixing device known in the industry, such as for example ascrew extruder, a Brabender mixer, a two-roll or a 3-roll mill.Alternatively, the noted components can be combined in a solvent andmixed using a mixer, or the dispersion can be sonicated, and cast,spray-coated, or otherwise coated onto a substrate or put into a mold,followed by evaporation of the solvent.

Thus, useful reactive fluoropolymer compositions of this inventioncomprise a fluoro-functionalized near-infrared radiation absorber thatis a fluoro-functionalized carbon black that is present in an amount ofat least 1 weight % and up to and including 35 weight %, based on thetotal dry reactive fluoropolymer composition weight.

Reactive fluoropolymers are compounds that are generally di-, tri-, ormulti-functional compounds that include two or more reactive groupsselected from the group consisting of reactive groups such asα,β-ethylenically unsaturated groups, hydroxy, carboxy, isocyanate,amine, thiol, carbonyl, alkene, vinyl, alkyne, epoxide, azide, boronicacid, and organic phosphates. Combinations of two or more of differentreactive groups can be present in the same multifunctional molecule. Insome embodiments, the reactive fluoropolymer is a multifunctional(meth)acrylate and the compound that causes crosslinking during thermalcuring is a peroxide, azo compound, persulfate, or redox initiator.

To form the fluoropolymers (such as elastomeric fluoropolymers), thereactive fluoropolymers are reacted during thermal curing of thereactive fluoropolymer composition to cause polymerization orcrosslinking, thereby forming the desired fluoropolymer (such as anelastomeric fluoropolymer). Thermal curing is facilitated using one ormore reactive compounds that are chosen so that they are reactive withthe reactive groups in the reactive fluoropolymer.

The reactive fluoropolymer composition comprises one or more compoundsthat cause crosslinking of the reactive fluoropolymer, for example whenusing a radical initiator, in an amount of at least 0.1 weight % and upto and including 5 weight %, and typically in an amount of at least 1weight % and up to and including 2 weight %, based on total reactivefluoropolymer composition dry weight. Alternatively, for example, whenusing an isocyanate crosslinker to react with a diol or amine reactivefluoropolymer, the equivalent molar ratio of alcohol (or amine) groupsand isocyanate groups would be about 1:1.

In some embodiments, the reactive fluoropolymer composition comprises areactive fluoropolymer that is a multifunctional (meth)acrylate and acompound that causes crosslinking during thermal curing that is aperoxide, azo compound, persulfate, or redox initiator.

Thus, thermally curing the reactive fluoropolymer composition canprovide a laser-engraveable composition comprising an elastomericfluoropolymer having a glass transition temperature (T_(g)) of less thanor equal to 0° C., and the fluoro-functionalized near-infrared radiationabsorber described above.

Suitable thermal curing conditions can be used as one skilled in the artwould know from the specific choice of reactive fluoropolymer (that is,the specific reactive groups) and a suitable compound that wouldfacilitate the thermal curing. For example, thermal curing can beachieved using an infrared dryer or heating unit, an oven, a rotocureunit, or in-line heating devices. For example, thermally curing thereactive fluoropolymer composition can be carried out in an oven at atemperature of at least 60° C. for at least 60 minutes, or when usingradical crosslinking, typically at a temperature of at least 70° C. andup to and including 90° C. for at least 30 minutes and up to andincluding 12 hours.

For example, if the reactive groups are vinyl groups (in acrylate ormethacrylate moieties), the compounds used to cause thermal curingprovide free radicals including but not limited to, peroxides or azocompounds such as benzoyl peroxide, tert-butyl peracetate, cumenehydroperoxide, cyclohexanone peroxide, dicumyl peroxide, lauroylperoxide, 2,4-pentanedione peroxide, di(t-butylperoxyisopropyl)benzene,2,5-dimethyl-2,5-bis(t-butyl) peroxy)hexane, bis(t-butylperoxy)-2,5-dimethyl-3-hexyne, t-butyl hydroperoxide,di(t-butyl) peroxide, n-butyl 4,4′-di(t-butylperoxy)valerate,1,1-bis(t-butylperoxy)-cyclohexane,1,1′-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, t-butyl cumylperoxide, t-butyl peroxybenzoate, t-butyl peroxy-2-ethylhexyl carbonate,2,2′-azobis(2-methylpropionitrile), 4,4-azobis(4-cyanovaleric acid),1,1′-azobis(cyclohexanecarbonitrile),2,2′-azobis(2-methylpropionamidine)dihydrochloride, persulfates, redoxinitiators, and any others that can react with carbon-carbon doublebonds to produce the desired curing (or crosslinking) density. The term“peroxide” also includes “hydroperoxides”. Many commercially availableperoxides are supplied at 40-50% activity with the remainder of thecommercial composition being inert silica or calcium carbonateparticles. The peroxide vulcanizing compositions generally also compriseone or more co-reagents at a molar ratio to the total peroxides of from1:6 to and including 25:1.

Vinyl groups can also be cured by metallocene catalysts, such astitanocene or zirconocene complexes. Vinyl groups can additionally becured by anionic polymerization using initiators including but notlimited to, sodium amide, lithium diethylamide, alkoxides, hydroxides,cyanides, phosphines, amines, alkyllithium compounds, andorganomagnesium compounds.

Co-reagents hat are useful with peroxides include but are not limitedto, triallyl cyanurate (TAC), triallyl isocyanurate, triallyltrimellitate, the esters of acrylic and methacrylic acids withpolyvalent alcohols, trimethylolpropane trimethacrylate (TMPTMA),trimethylolpropane triacrylate (TMPTA), ethylene glycol dimethacrylate(EGDMA), and N,N′-m-phenylenedimaleimide (HVA-2, DuPont).

The continuous laser-engraveable layer (for example, on a fabric webwith the compressible layer) can then be laminated (or adhered) to asuitable polymeric film such as a polyester film to provide thelaser-engraveable layer on a substrate, for example, a fabric webadhered with an adhesive to the polyester film. The continuouslaser-engraveable layer can be ground using a suitable grindingapparatus to provide a uniform smoothness and thickness in thecontinuous laser-engraveable layer. The smooth, uniformly thicklaser-engraveable layer can then be cut to a desired size to providesuitable laser-engraveable elements such as flexographic printingprecursors.

The process for making flexographic printing sleeves is similar but thecompounded laser-engraveable layer composition can be applied ordeposited around a printing sleeve core, and cured to form a continuouslaser-engraveable flexographic printing sleeve precursor.

Similarly, a continuous calendered laser-engraveable layer on a fabricweb can be deposited around a printing cylinder and cured to form acontinuous flexographic printing cylinder precursor.

Various embodiments of laser-engraveable elements can be prepared by themethod described herein. For example, the method can comprise:

forming the reactive fluoropolymer composition into a reactivefluoropolymer layer over a substrate, and

thermally curing the reactive fluoropolymer layer to provide alaser-engraveable layer over the substrate. In many embodiments, thereactive fluoropolymer composition is formed directly on the substrateand then thermally cured. In other embodiments, there can be one or morelayers between the substrate and the formed reactive fluoropolymerlayer.

As noted above, useful substrates for these methods can be selected fromthe group consisting of a polymeric film, a fabric-containing web, aceramic, a metal, and glass including flexible glass. Particularlyuseful substrates include fabric-containing webs, such as laminates offabrics and polymeric films, to which the reactive fluoropolymercomposition is applied prior to thermally curing it to form thelaser-engraveable layer on the fabric-containing web.

In other embodiments, the method comprises forming a reactivefluoropolymer composition in a mold prior to thermally curing thereactive fluoropolymer composition to form a laser-engraveable layer inthe mold.

In still other embodiments, the method comprises:

applying a non-laser-engraveable composition (as described above, forexample, a compressible layer composition) over a substrate to form anon-laser-engraveable layer over the substrate,

applying a reactive fluoropolymer composition to thenon-laser-engraveable layer, and

thermally curing the reactive fluoropolymer composition to form alaser-engraveable layer on the non-laser-engraveable layer.

If the laser-engraved element is designed to have two or morelaser-engraveable layers, the method comprises:

applying a reactive fluoropolymer composition over a substrate,

before or after applying the reactive fluoropolymer composition over thesubstrate, applying an additional reactive fluoropolymer compositionover the substrate,

wherein the reactive fluoropolymer composition and the additionalreactive fluoropolymer composition have the same or different chemicalcomposition, and

thermally curing both the reactive fluoropolymer composition and theadditional reactive fluoropolymer composition to form first and secondlaser-engraveable layers over the substrate.

This process can be repeated as many times as desired to form three ormore laser-engraveable layers of this invention over the substrate,which laser-engraveable layers can be contiguous, or any twolaser-engraveable layers of this invention can be separated byintermediate layers that are either laser-engraveable or notlaser-engraveable, but which intermediate layers do not contain afluoropolymer.

Laser-Engraving for Imaging

Laser engraving can be accomplished using a near-IR radiation emittingdiode or carbon dioxide or Nd:YAG laser. It is desired to laser engravethe laser-engraveable layer to provide a relief image with a minimumrelief image depth of at least 10 μm and up to and including 4,000 μm,or of at least 50 μm and up to and including 1,000 μm. For flexographicprinting members, more likely, the minimum relief image depth is atleast 300 μm and up to and including 4,000 μm or up to and including1,000 urn being desirable. “Relief floor depth” is defined as thedifference measured between the floor (lowest engraved areas) of thelaser-engraved element and its outermost printing surface. It is to beunderstood that the relief image depth between image features (reliefimage depth, which is defined as the difference measured between thebottom of a specific laser-engraved area and its outermost printingsurface) that are closely spaced will be less than the relief floordepth. The floor of the relief image can be the substrate if all layersare completely removed in the imaged regions. A semiconductornear-infrared radiation laser or one or more (array) of such lasersoperating at a wavelength of at least 700 nm and up to and including1400 nm can be used, and a diode laser operating at from 800 nm to 1250nm is particularly useful for laser-engraving.

Generally, laser-engraving is achieved using at least one near-infraredradiation laser having a minimum fluence level of at least 1 J/cm² atthe element topmost and typically near-infrared imaging fluence is atleast 20 J/cm² and up to and including 1,000 J/cm² or typically at least50 J/cm² and up to and including 800 J/cm².

For example, laser-engraving can be carried out using a diode laser, anarray of diode lasers connected with fiber optics, a Nd-YAG laser, afiber laser, a carbon dioxide gas laser, or a semiconductor laser. Suchinstruments and conditions for their use are well known in the art andreadily available from a number of commercial sources. Detaileddescriptions can be found in U.S. Patent Application Publications2010/0068470A1 (Sugasaki), 2008/018943A1 (Eyal et al.), and2011/0014573A1 (Matzner et al.), all hereby incorporated by reference.

A suitable laser engraver that would provide satisfactory engraving isdescribed in WO 2007/149208 (Eyal et al.) that is incorporated herein byreference. This laser engraver is considered to be a “high powered”laser ablating imager or engraver and has at least two laser diodesemitting radiation in one or more near-infrared radiation wavelengths sothat imaging with the one or more near-infrared radiation wavelengths iscarried out at the same or different depths relative to the outersurface of the laser-engraveable layer. For example, the multi-beamoptical head described in the noted publication incorporates numerouslaser diodes, each laser diode having a power in the order of at least5-10 Watts per emitter width of 100 μm. These lasers can be modulateddirectly at relatively high frequencies without the need for externalmodulators.

Thus, laser-engraving (laser imaging) can be carried out at the same ordifferent relief image depths relative to the outer surface of thelaser-engraveable layer using two or more laser diodes, each laser diodeemitting near-infrared radiation in one or more wavelengths.

Other imaging (or engraving) devices and components thereof and methodsare described for example in U.S. Patent Application Publications2008/0153038 (Siman-Tov et al.) describing a hybrid optical head fordirect engraving, 2008/0305436 (Shishkin) describing a method of imagingone or more graphical pieces in a flexographic printing plate precursoron a drum, 2009/0057268 (Aviel) describing imaging devices with at leasttwo laser sources and mirrors or prisms put in front of the lasersources to alter the optical laser paths, and 2009/0101034 (Aviel)describing an apparatus for providing an uniform imaging surface, all ofwhich publications are incorporated herein by reference. In addition,U.S. Patent Application Publication 2011/0014573 (Matzner et al.)describes an engraving system including an optical imaging head, aprinting plate construction, and a source of imaging near-infraredradiation, which publication is incorporated herein by reference. U.S.Patent Application Publication 2011/0058010 (Aviel et al.) describes animaging head for 3D imaging of flexographic printing plate precursorsusing multiple lasers, which publication is also incorporated herein byreference.

Engraving to form a relief image can occur in various contexts. Forexample, the laser-engraved elements can have a relief image having aminimum relief image depth of at least 10 μm, and the relief image layercomprises a fluoropolymer (such as an elastomeric fluoropolymer) asdescribed above, and at least 1 weight % of a fluoro-functionalizednear-infrared radiation absorber (as described above), based on thetotal dry relief image layer weight. This relief image layer can bedisposed over a substrate (such as polymeric film, a fabric-containingweb, a ceramic, a metal, and glasses such as flexible glasses). Forexample, sheet-like elements can be imaged and used as desired, orwrapped around a printing sleeve core or cylinder form before imaging.The laser-engraved elements having a relief image layer can beflexographic printing plates, flexographic printing sleeves, orflexographic printing cylinders.

During imaging, products from the engraving can be gaseous or volatileand readily collected by vacuum for disposal or chemical treatment. Anysolid debris from engraving can be collected and removed using suitablemeans such as vacuum, compressed air, brushing with brushes, rinsingwith water, blotting with an absorbent material, ultrasound, or anycombination of these.

During printing, the resulting flexographic printing plate,laser-engraved element, or patterned element, flexographic printingcylinder, or printing sleeve is typically inked using known methods andthe ink is appropriately transferred to a suitable receiver materialsuch as papers, plastics, fabrics, paperboard, metals, particle board,wall board, glass, glass-coated substrates, ceramics, or cardboard.

After printing, the laser-engraved element can be cleaned and reused ina suitable manner and reused as needed. Cleaning can be accomplishedwith compressed air, water, or a suitable aqueous or organic solution,or by rubbing with cleaning brushes or pads. Surfactants or soaps can beadded to the aqueous or organic solutions to accelerate cleaning.

Other laser-engraved elements can be used to apply ink patterns tovarious substrates using a suitable pattern-forming material (or ink)such as a flexographic printing ink, an electrically conductive ink(such as a silver-containing ink, nickel-containing ink, orcopper-containing ink, or metal salts or metal precursors, such assilver salts), a seed or catalyst or growth agent, or a biologicalagent-containing ink. In the context of this invention, the term “ink”is to be understood to broadly refer to a substance or fluid that can be“printed” or applied to a receiver material of any type using thelaser-engraved element. A skilled artisan would be able to apply thepresent invention to various printing technologies using suitable inksto provide desired patterns (for example, conductive patterns), grids,or raised surfaces that “correspond” to the relief image in thelaser-engraved element.

In some embodiments, the laser-engraved element can be have a reliefimage layer comprising a predetermined pattern of relief lines, eachline having an average width of at least 1 μm and up to and including 10mm. Such lines can also have an average height of at least 10 μm and upto and including 4,000 μm. These average dimensions can be determined bymeasuring the lines in at least 10 places and determining the width orheight using known image analysis tools including but not limited to,profilometry, optical microscopic techniques, atomic force microscopy,and scanning electron microscopy.

The present invention provides at least the following embodiments andcombinations thereof, but other combinations of features are consideredto be within the present invention as a skilled artisan would appreciatefrom the teaching of this disclosure:

1. A composition comprising:

1) a fluoropolymer, and

2) at least 1 weight % of a fluoro-functionalized near-infraredradiation absorber, based on the total dry composition weight.

2. The composition of embodiment 1, wherein the fluoro-functionalizednear-infrared radiation absorber is a fluoro-functionalized carbonblack, fluoro-functionalized carbon nanotube, fluoro-functionalizedgraphene, or fluoro-functionalized dye, or a mixture or combination ofany of these materials.

3. The composition of embodiment 1 or 2, wherein thefluoro-functionalized near-infrared radiation absorber is afluoro-functionalized carbon black that is present in an amount of atleast 1 weight % and up to and including 35 weight %, based on the totaldry composition weight.

4. The composition of any of embodiments 1 to 3, wherein thefluoropolymer is present in an amount of at least 30 weight % and up toand including 99 weight %, based on the total dry composition weight.

5. The composition of any of embodiments 1 to 4, wherein thefluoropolymer is an elastomeric fluoropolymer.

6. The composition of embodiment 5, wherein the elastomericfluoropolymer has a glass transition temperature (T_(g)) of less than orequal to 0° C.

7. The composition of any of embodiments 1 to 6, wherein thefluoropolymer is an elastomeric perfluoropolyether.

8. The composition of any of embodiments 1 to 7 consisting essentiallyof the fluoropolymer that is an elastomeric fluoropolymer and thefluoro-functionalized near-infrared radiation absorber.

9. The composition of any of embodiments 1 to 8, further comprising oneor more materials selected from the group consisting of hollow, solid,or porous particles, surfactants, plasticizers, lubricants,non-fluorinated resins, and microspheres.

10. The composition of embodiment 9, wherein the one or more materialsare present in the composition in an amount of up to and including 50weight %, based on total dry composition weight.

11. The composition of any of embodiments 1 to 10, wherein the weightratio of the fluoropolymer to the fluoro-functionalized near-infraredabsorber is from 99:1 to and including 1.4:1.

12. A reactive fluoropolymer composition comprising a reactivefluoropolymer, a fluoro-functionalized near-infrared radiation absorber,and a compound that causes crosslinking of the reactive fluoropolymerduring thermal curing.

13. The reactive fluoropolymer composition of embodiment 12, wherein thefluoro-functionalized near-infrared radiation absorber is afluoro-functionalized carbon black, fluoro-functionalized carbonnanotube, fluoro-functionalized graphene, or fluoro-functionalized dye,or a mixture or combination of any of these materials.

14. The reactive fluoropolymer composition of embodiment 12 or 13,wherein the fluoro-functionalized near-infrared radiation absorber is afluoro-functionalized carbon black that is present in an amount of atleast 1 weight % and up to and including 35 weight %, based on the totaldry composition weight.

15. The reactive fluoropolymer composition of any of embodiments 12 to14, further comprising one or more materials selected from the groupconsisting of hollow, solid, or porous particles, surfactants,plasticizers, lubricants, non-fluorinated resins, and microspheres.

16. The reactive fluoropolymer composition of any of embodiments 12 to15, wherein the reactive fluoropolymer comprises one or more reactivegroups selected from the group consisting of α,β-ethylenicallyunsaturated groups, hydroxy, carboxy, isocyanate, (meth)acrylate, amine,thiol, carbonyl, alkene, alkyne, epoxide, azide, boronic acid, andorganic phosphate groups.

17. The reactive fluoropolymer composition of any of embodiments 12 to16, wherein the reactive fluoropolymer has a number average molecularweight of at least 1000 g/mol.

18. The reactive fluoropolymer composition of any of embodiments 12 to17, wherein the compound that causes crosslinking of the reactivefluoropolymer is present in an amount of at least 0.1 weight % and up toand including 5 weight %.

19. The reactive composition of any of embodiments 12 to 18, wherein thereactive fluoropolymer is a multifunctional (meth)acrylate and thecompound that causes crosslinking during thermal curing is a peroxide,azo compound, persulfate, or redox initiator.

20. A method for providing a laser-engraveable composition, comprising:

combining a reactive fluoropolymer, a fluoro-functionalizednear-infrared radiation absorber, and a compound that causescrosslinking of the reactive fluoropolymer during thermal curing, toform a reactive fluoropolymer composition of any of embodiments 12 to19, and

thermally curing the reactive fluoropolymer composition to provide alaser-engraveable composition comprising a fluoropolymer and thefluoro-functionalized near-infrared radiation absorber.

21. The method of embodiment 20, wherein thermally curing the reactivefluoropolymer composition provides a laser-engraveable compositioncomprising an elastomeric fluoropolymer having a glass transitiontemperature (T_(g)) of less than or equal to 0° C., and thefluoro-functionalized near-infrared radiation absorber.

22. The method of embodiment 20 or 21, wherein the reactivefluoropolymer is a multifunctional (meth)acrylate and the compound thatcauses crosslinking during thermal curing is a peroxide, azo compound,persulfate, or redox initiator.

The following Examples are provided to illustrate the practice of thisinvention and are not meant to be limiting in any manner.

The following materials, 2,2′-azobis(2-methylpropionitrile) (AIBN),chloroform, 2-isocyanatoethyl methacrylate,1,1,2-trichloro,-1,2,2-trifluoroethane, dibutyltin dilaurate (DBTDL),and poly(tetrafluoroethylene oxide-co-difluoromethylene oxide) α,ω-diol,were purchased from Sigma-Aldrich Chemical Co. and used as received.

Preparation of Reactive Fluoropolymer:

A perfluoropolyether bisurethane methacrylate oligomer was prepared asfollows:

Poly(tetrafluoroethylene oxide-co-difluoromethylene oxide) α,ω-diol(34.6 g, 0.009 mol), 2-isocyanatoethyl methacrylate (2.82 g, 0.018 mol),and DBTDL (7 drops) were dissolved in1,1,2-trichloro,-1,2,2-trifluoroethane (10 ml) and heated to 50° C. for24 hours. The resulting oligomer was then passed through a short columnof basic alumina, concentrated, and placed under vacuum to dry whichyielded a dry pale yellow solid (34.3 g, 99% yield).

Preparation of Fluoro-Functionalized Near-Infrared Radiation Absorber:

Carbon black (10 g of Cabot R330A67) was added to 100 ml of water andstirred using a Cowles-type blade powered by an overhead shaft-drivenmotor operating at 500 rpm to form a carbon black slurry. Mixing wascontinued for 1 hour. Meanwhile, a solution of 3-trifluoromethylbenzenediazonium chloride was prepared by dissolving 0.64 g (0.004 mol) ofm-trifluoromethyl-aniline in 10 ml of water containing 1.5 ml ofconcentrated HCl, chilling the solution to less than about 10° C. usingan ice bath, and then adding 0.3 g (0.0043 mol) of sodium nitrite in 5ml of water. The resulting mixture was stirred cold for 30 minutes and30 mg of urea were added to decompose any excess nitrous acid. Theresulting solution was added to the carbon black slurry and stirring wascontinued at ambient temperature for about 3 hours. Some gas evolutionwas noted.

The fluoro-functionalized carbon black product was collected byfiltration through a fine glass frit funnel, and rinsed with several50-100 ml portions of water followed by about 25 ml of methanol. Afterthe resulting solid had dried, it was transferred to a Soxhlet thimbleand extracted using hot acetone for 4 hours. The purified carbon blackproduct was dried at 50° C. under vacuum to yield 10.1 g of product.

The fluoro-functionalized carbon black product was dry ground using aTekmar-type blade mill for about 1 minute in order to break up anylarger clumps.

Invention Example E1

Perfluoropolyether bisurethane methacrylate oligomer (1.69 g) wassonicated with the fluoro-functionalized carbon black product describedabove (0.085 g) as described in U.S. Pat. No. 6,399,202 (Yu et al.).AIBN (0.02 g, 1.2 weight %) was dissolved in chloroform (3-4 drops) andimmediately added to the reactive fluoropolymer mixture. An additionalamount of chloroform (2 drops) was added to the AIBN-containing beakerand the wash was subsequently added to the resulting laser-engraveablecomposition. After stirring, the laser-engraveable composition was knifecast onto Kapton™ 200-1-IN as a substrate, clamped securely to a metalplate, and placed in a heating oven with a nitrogen purge at 90° C. for5 hours or until the resulting laser-engraveable element was fullycured.

Comparative Example CE1

Perfluoropolyether bisurethane methacrylate oligomer (1.69 g) wassonicated with Cabot Mogul® L carbon black (5 weight %). AIBN (1.2weight %) was dissolved in several drops of chloroform and added to theresulting reactive fluoropolymer mixture. After stirring, the resultinglaser-engraveable composition was knife cast onto Kapton™ 200-HN as asubstrate, clamped securely to a metal plate, and placed in a heatingoven with a nitrogen purge at 90° C. until the resultinglaser-engraveable element was fully cured.

Comparative Example CE2

Perfluoropolyether bisurethane methacrylate oligomer (1.68 g) wassonicated with Cabot Regal® 330 A67 carbon black (5 weight %). AIBN (1.2weight %) was dissolved in several drops of chloroform and added to theresulting reactive fluoropolymer mixture. After stirring, the resultinglaser-engraveable composition was knife cast onto Kapton™ 200-HN as asubstrate, clamped securely to a metal plate, and placed in a heatingoven with a nitrogen purge at 90° C. until the resultinglaser-engraveable element was fully cured.

Comparative Example CE3

Perfluoropolyether bisurethane methacrylate oligomer (1.72 g) wassonicated with Cabot Regal® 330 A67 carbon black (5 weight %) that hadbeen previously ground with a Tekmar-type blade mill. AIBN (1.2 weight%) was dissolved in several drops of chloroform and added to theresulting reactive fluoropolymer mixture. After stirring, the resultinglaser-engraveable composition was knife cast onto Kapton™ 200-HN as asubstrate, clamped securely to a metal plate, and placed in a heatingoven with a nitrogen purge at 90° C. until the resultinglaser-engraveable element was fully cured.

Laser Engraving:

Each laser-engraveable element was laser engraved using a continuouswave (CW) laser operating in the 830 nm range at 25 Watts in 960channels. The laser beam has a 3 μm spot size (Kodak SQUAREspot®technology) at optimum focus. Each laser-engraveable element was mountedon a flat plate that moved in the Y (fast scan) direction while thelaser head moved on an air bearing in the X (slow scan) direction. Pixelplacement was on 2 μm centers corresponding to an addressability of12800 dpi. Imaging was performed at 0.2 msec and the correspondingfluence was calculated to be 19.7 J/cm² for the sum of the 3 consecutivepasses. The resulting laser-engraved relief images were examined using ascanning electron microscope.

TABLE I below provides some details about the laser-engraveable elementsand TABLE II provides properties of the resulting laser-engravedelements.

TABLE I Visual Quality of Laser-Engraveable Elements Smoothness QualityPrecursor Example Carbon Black Employed Score E1 Cabot Regal ® 330 A67 3(Fluorinated) CE1 Mogul ® L 2 CE2 Cabot Regal ® 330 A67 1 CE3 CabotRegal ® 330 A67 3 (Ground)

The Smoothness Quality Score was quantified visually as follows:

3=Smooth laser-engraveable element of high quality that cured with veryfew bumps and pits.

2=Relatively smooth laser-engraveable element of medium quality thatcured with some noticeable bumps and pits.

1=Very rough laser-engraveable element of poor quality that cured poorlywith obvious phase separation, bumps, and pits.

TABLE II Engraved Quality Ablation (engraved) Example Carbon BlackEmployed score E1 Cabot Regal ® 330 A67 3 (Fluorinated) CE1 Mogul ® L 2CE2 Cabot Regal ® 330 A67 1 CE3 Cabot Regal ® 330 A67 2 (Ground)

The Ablation Quality was quantified visually from the laser-engravedelements that were imaged by scanning electron microscopy (SEM) wherein:

3=Well-defined laser-engraved features in the relief image, with arelatively smooth floor.

2=Some well-defined laser-engraved features in the relief image, withobvious bumps and porosity in the floor.

1=Poorly defined laser-engraved features with little to no relief image.

These results illustrate that only the compositions of thefluoropolymers that include the near-infrared radiation absorber thathas been fluoro-functionalized according to this invention provide goodquality precursors that can be laser engraved to provide precise qualityimage features with good relief.

Contact Angles:

Static contact angle measurements of water droplets on thelaser-engraveable elements described above were obtained at 22° C. inair using a pendant drop delivered from an automated syringe pump in anFTA 200 system designed for contact angle determination. Each drop wasplaced controllably on the laser-engraveable surface of eachlaser-engraveable element. The results are shown below in TABLE III andcompared to results obtained for commercially available flexographicprinting plate precursors.

These results show surface energy modification by an increase in thewater contact angle after creation of the fluorinated laser-engraveableelement when compared to commercially available flexographic printingplate precursors outside of this invention.

TABLE III Contact Angle Water Contact Angle Precursor Description (°) E1Perfluoropolyether with 111.2 Cabot Regal ® 330 A67 (Fluorinated) CE1Perfluoropolyether with 114.0 Mogul ® L CE2 Perfluoropolyether with109.6 Cabot Regal ® 330 A67 CE3 Perfluoropolyether with 116.2 CabotRegal ® 330 A67 (Ground) CE4 Laserflex ® FP6001 from 87.0 FulflexFlexographic Systems flexographic printing plate precursor CE5 Flexcel ®flexographic 70.8 printing plate precursor (Eastman Kodak)

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

1. A laser-engraveable element comprising a thermally crosslinkedlaser-engraveable layer comprising a crosslinked elastomericfluoropolymer and a fluoro-functionalized near-infrared radiationabsorber, the crosslinked fluoropolymer having a glass transitiontemperature of less than and including 0° C., the crosslinkedlaser-engraveable layer being formed from a reactive fluoropolymercomposition comprising a reactive fluoropolymer, thefluoro-functionalized near-infrared radiation absorber, and a compoundthat causes crosslinking of the reactive fluoropolymer during thermalcuring, wherein the reactive fluoropolymer comprises one or morereactive groups selected from the group consisting of:poly(tetrafluoroethylene oxide-co-difluoromethylene oxide) α,ω-diolbis(2,3-dihydroxypropyl ether), poly(tetrafluoroethyleneoxide-co-dilfluoromethylene oxide) α,ω-diol, ethoxylatedpoly(tetrafluoroethylene oxide-co-difluoromethylene oxide) α,ω-diol, anda multifunctional (meth)acrylate end-functionalized derivative of one ofsuch compounds.
 2. The laser-engraveable element of claim 1, wherein thefluoro-functionalized near-infrared radiation absorber is afluoro-functionalized carbon black, fluoro-functionalized carbonnanotube, fluoro-functionalized graphene, or fluoro-functionalized dye,or a mixture or combination of any of these materials.
 3. Thelaser-engraveable element of claim 1, wherein the fluoro-functionalizednear-infrared radiation absorber is a fluoro-functionalized carbon blackthat is present in an amount of at least 1 weight % and up to andincluding 35 weight %, based on the total dry reactive fluoropolymercomposition weight.
 4. The laser-engraveable element of claim 1, furthercomprising one or more materials selected from the group consisting ofhollow, solid, or porous particles, surfactants, plasticizers,lubricants, non-fluorinated resins, and microspheres, in the crosslinkedlaser-engraveable layer.
 5. The laser-engraveable element of claim 1,wherein the reactive fluoropolymer has a number average molecular weightof at least 1000 g/mol.
 6. The laser-engraveable element of claim 1,further comprising a substrate on which the thermally crosslinkedlaser-engraveable layer disposed.
 7. The laser-engraveable element ofclaim 6, further comprising an elastomeric rubber compressible layerbetween the substrate and the thermally crosslinked laser-engraveablelayer.
 8. The laser-engraveable element of claim 6, further comprising aconductive layer between the substrate and the thermally crosslinkedlaser-engraveable layer.
 9. The laser-engraveable element of claim 6,wherein the substrate comprises a polyimide, polyester, or a fabric webadhered to a polyester film.
 10. The laser-engraveable element of claim9, further comprising an elastomeric rubber compressible layer betweenthe substrate and the thermally crosslinked laser-engraveable layer. 11.The laser-engraveable element of claim 1, wherein the crosslinkedfluoropolymer is present in an amount of at least 30 weight % and up toand including 99 weight %, based on the total weight of the thermallycrosslinked laser-engraveable layer.
 12. The laser-engraveable elementof claim 1, wherein the crosslinked fluoropolymer has a glass transitiontemperature of at least −100° C. and up to and including 0° C.
 13. Thelaser-engraveable element of claim 1, wherein the weight ratio of thecrosslinked fluoropolymer to the fluoro-functionalized near-infraredradiation absorber being from 19:1 to and including 4:1.
 14. Thelaser-engraveable element of claim 6, further comprising a conductivelayer disposed between the substrate and the laser engraveable layer.15. A method for providing a relief image, comprising: laser-engravingthe laser-engraveable element of claim 1, to provide a laser-engravedelement having a relief image having a minimum depth of 10 μm in thelaser-engraveable layer.
 16. The method of claim 15, wherein thelaser-engraving is carried out using one or more near-infrared radiationemitting lasers.
 17. The method of claim 15, further comprising:printing an ink pattern using the laser-engraved element.
 18. The methodof claim 15, further comprising: printing an electrically conductive inkto form a patterned conductive article using the laser-engraved element.19. The method of claim 15, further comprising: printing a pattern witha silver-containing ink to form a patterned conductive article using asilver-containing conductive ink.
 20. The method for making a device,comprising: incorporating the patterned conductive article formed inclaim 18 into an optical device, solar panel, display device, medicaldevice, or electronic device.